Submicron-porous Al₂O₃-MgAl₂O₄ Composite With Slag Penetration Resistance And Its Effect On The Properties Of Working Lining Castables For Steel Ladle

Ladle is an important equipment for storage,transfer and refining of molten steel in steelmaking process.As thermal properties of the steel ladle refractory lining are rigorously associated with the ladle ability to keep the molten steel temperature constant,the steel ladle lining refractories are expected to have excellent high-temperature performance as well as low thermal conductivity.To improve the energy efficiency,and reduce the environmental impacts,the replacement of dense aggregates with porous ones in ladle working layer refractories to improve thermal properties of the steel ladle refractory lining was suggested and explored.Compared to its conventional counterpart using tabular corundum aggregate,the lightweight alumina-magnesia castable using porous aggregates showed lower thermal conductivity and well-matched corrosion performance,but deteriorated penetration resistance.To solve this problem,a novel chemical-mineralogical gradient submicron-porous corundum-spinel composite has been engineered and prepared in lab and industrial trial production.In such a composite,composition gradient spinel particles were in situ formed/embedded on the inner surfaces of pores,forming special gradient spinel particles surrounding the pore structure.On the other hand,to optimize and improve the properties of the castable matrix,an active corundum-spinel micro-powder was developed and produced as well.Corrosion of the chemical-mineralogical gradient submicron-porous corundum-spinel composites in contact with molten converter terminal slag was examined in detail,and compared with in the case of sintered corundum.Furthermore,the penetration-corrosion mechanisms in both cases were also discussed and compared,the matrix formulation and properties of castables were engineered and investigated by using active corundum-spinel powder,the low thermal conductivity castables for ladle working lining based on the chemical-mineralogical gradient submicron-porous corundum-spinel aggregates were developed,and the temperature field of the ladle were simulated and analyzed.Based on the above work,the corundum-spinel precasted castable blocks were prepared by using the chemical-mineralogical gradient submicron-porous corundum-spinel aggregates with bulk density of 3.08g/cm³,and the application test was carried out in the steel plant.The following conclusions can be drawn:（1）Different from the traditional single-phase porous materials,the composites have special gradient spinel particles surrounding the pore structure.The bulk densities of the composites are 3.08-3.09g/cm³,the total porosities of the composites are 10.6-19.2%,the thermal conductivity of the as prepared composites at 800°C decreased 30-46%compared to their sintered corundum counterpart.（2）The slag penetration and corrosion resistance of the chemical-mineralogical gradient submicron-porous corundum-spinel composites are superior to in the case of the sintered corundum.This is attributed to the special submicron-pore structure,the chemical-mineralogical gradient Al₂O₃-rich spinel particles pre-embedded on the inner-surfaces of the pores,in the corundum matrix of the former,which is believed to be essential for absorption of Fe²⁺and Fe³⁺and precipitation of complex spinel（Mg,Fe）（Al,Fe）₂O₄ from the liquid slag and further enhance the anti-slag-penetration function of the pores.Upon the molten slag infiltration into the special submicron-pores in the corundum matrix of the composites and came into contact and reacted with the chemical-mineralogical gradient Al₂O₃-rich spinel pre-embedded on the inner surface of the pores,sufficient amounts of gradient Al₂O₃-rich spinels pre-embedded on the inner surfaces of the pores dissolved into the molten slag at 1600°C,leading to formation and precipitation of complex spinel（Mg,Fe）（Al,Fe）₂O₄,making the slag deficient in Fe²⁺and Fe³⁺and rich in Ca O.Corundum matrix in the composites reacted with Ca O from the Ca O-rich liquid slag,building up a continuous dense layer of tightly interlocked highly refractory tabular Ca A1₁₂O₁₉,contributing considerably to the improved penetration resistance of the pore regions in the composites,and suppressing the further slag penetration and corrosion.（3）The fluidity and sintering properties of castables matrix were optimized and the matrix formulation were determined by studying the rheological properties of the fine powder suspension and designing the matrix formulation.（4）The low thermal conductivity castables,prepared by partial or total replacement of the sintered corundum with the chemical-mineralogical gradient submicron-porous corundum-spinel composite with bulk density of 3.08g/cm³ and 3.39g/cm³,respectively,have good mechanical properties,lower thermal conductivity（comparing with the conventional castable）and good corrosion performance,well-matched the traditional corundum-spinel castable.（5）The finite element simulation results show that the lowest temperature of ladle outer surface declined about 60°C using the as-prepared castables compared with the traditional castables.（6）Application results in the first Steel Plant of Baowu Steel Group Co.,Ltd show that the castable blocks with chemical mineralogical gradient submicron-porous corundum-spinel aggregate with 3.08 g/cm³ had good slag erosion and penetration resistance.